Field of the Invention
The present invention relates to a circumference coating material, a bonding material, a honeycomb structure, and a method of producing the honeycomb structure. More specifically, the present invention relates to a circumference coating material, a bonding material, a honeycomb structure, and a method of producing the honeycomb structure that are free from corrosion of metal products or metal parts such as exhaust system pipes.
Description of the Related Art
Heretofore, a ceramic honeycomb structure has been used for a wide range of applications such as a catalyst carrier for purifying vehicle exhaust gases, a diesel particulate removing filter, or a heat storage body for a combustion apparatus. The ceramic honeycomb structure (hereinafter, simply referred to as a “honeycomb structure”) is produced by preparing a forming material (kneaded material), extruding the forming material into a desired honeycomb shape using an extruder, intactly cutting, drying, and finishing the extruded forming material to a honeycomb formed body, and firing the honeycomb formed body at a high temperature. The honeycomb structure includes a partition wall that defines a plurality of polygonal lattice cells extending from one end face to the other end face which form a through channel of a fluid.
The honeycomb structure used as a catalyst carrier for purifying vehicle exhaust gases for a large vehicle such as a truck or a diesel black-smoke particulate removing filter requires a large diameter. Even in the honeycomb structure of the large diameter, the forming material can be monolithically formed into a desired shape using an extruder, but the entire honeycomb structure deforms or a part of a cell structure deforms or collapses by its own weight immediately after extrusion. In order to remove such deformation or collapse, a circumferential surface is ground after firing, and a circumference coating material is applied to the ground circumferential surface to provide a circumferential wall, and obtain a honeycomb structure of a desired shape (for example, a round pillar-shape).
Particularly, in order to improve performance of purifying vehicle exhaust gases, a tendency of a lower bulk density of the honeycomb structure such as high porosity of the honeycomb structure or thinner partition walls in the honeycomb structure is strongly required. The lower bulk density of the honeycomb structure makes it difficult to maintain a honeycomb shape immediately after extrusion and lowers mechanical strength of the honeycomb structure. For this reason, by the lower bulk density of the honeycomb structure which can be monolithically formed at a traditional bulk density, circumference grinding and circumference coating are required, and the circumference grinding and the circumference coating are also gradually required for a compact honeycomb structure.
In a case where a high heat-resistance material such as SiC is used for a material of the honeycomb structure, since the thermal expansion of the material is large, cracks occur due to temperature gradients in use when the honeycomb structure is monolithically formed. In order to prevent the occurrence of cracks, a plurality of quadrangular pillar-shaped honeycomb fired bodies (honeycomb segments) is made in advance, and a bonding material is applied to side surfaces (bonding surfaces) of the obtained honeycomb segments, and the plurality of honeycomb segments is laminated and bonded to each other in combination, thereby forming one large block-shaped honeycomb structure (honeycomb block body). Thereafter, a circumferential surface of the honeycomb block body is ground, and the honeycomb structure is worked into a desired shape (for example, a round pillar-shape).
By the grinding, a cell on the circumferential surface of the honeycomb structure is in a state where a partition wall located between the cell and the outside is removed in total or in part. Therefore, an imperfect partition wall opened to the outside and extending in an axial direction is exposed. The imperfect partition wall is easily peeled off by an external force. Accordingly, in order to protect the circumferential surface of the honeycomb structure and maintain the shape, a circumference coating material is applied to the circumferential surface of the honeycomb structure and is subjected to drying, whereby a circumferential wall is formed (for example, see Patent Document 1). That is, it is necessary to use a circumference coating material in the production of a large-sized honeycomb structure having a large honeycomb diameter, and it is necessary to use a bonding material and a circumference coating material in the case of combining a plurality of honeycomb segments to constitute a honeycomb structure.
[Patent Document 1] JP-B2-2613729